Silicon optical chip twists beams of light

(Nanowerk News) University of Glasgow scientists have helped to create silicon optical chips to generate twisted beams of light which could be used to manipulate tiny particles or increase the capacity of optical communications technology.

A recent paper published in the journal Science ("Integrated Compact Optical Vortex Beam Emitters") outlines how an international research team involving the Universities of Glasgow and Bristol, along with colleagues at the Universities of Sun Yat-Sen and Fudan in China, have demonstrated integrated arrays of ‘optical vortex beams’ on a silicon chip.

Dr Michael Strain, research associate in Electronic and Nanoscale Engineering at the University, said: “The energy of the light in an optical vortex beam travels in a spiral, creating a hollow conical beam that looks much like a mini-vortex. When light in such beams interacts with matter it asserts a rotational force, making it useful as an ‘optical spanner’ or ‘optical tweezers’, which can rotate, as well as trap microscopic particles, droplets or single cells.

“In addition, the different amounts of twist generated in the beam can be used to carry information, and so the capacity of a single communications channel can be greatly enhanced by transmitting signals with different values of twist at the same time.”

Dr Marc Sorel, Senior Lecturer in Electronic and Nanoscale Engineering said: “A key issue for many applications is not just the ability to create beams with optical angular momentum but also the ability to integrate such optical vortex emitters into photonic circuits.

“Previously, bulky laboratory equipment and sensitive optical alignment tools were required to produce optical vortex beams. At the University of Glasgow’s world-leading James Watt Nanofabrication Centre, we created tiny silicon wires and micro ring resonators just a few thousandths of a millimetre in diameter which can produce the same effect.”

These components are characteristic of the guided wave photonic circuit technology that has been developed at Glasgow for applications from telecommunications to sensing.

Dr Strain added: “In the case of the vortex beam emitters, when photons are trapped inside a ring, they interact with nano-patterned corrugations in the ring's surface and are forced into vertically emitted vortex beams. By integrating tiny micro-ring emitters on a silicon chip many of them can be generated in a single shot and can be interfaced with existing photonic circuit designs in very small packages.”

Siyuan Yu, Professor of Photonics Information Systems in the Photonics Research Group at the University of Bristol, who led the research, said: “Our microscopic optical vortex devices are so small and compact that silicon micro-chip containing thousands of emitters could be fabricated at very low costs and in high volume.

“Such integrated devices and systems could open up entirely new applications of optical vortex beams previously unattainable using bulk optics.”